The present invention relates to improvements in centrifugal impact rock crushers, and particularly to feed apparatus for use in such rock crushers to improve the pattern of abrasive wear on replaceable portions of the rock crushers in order to reduce the frequency of need for replacement of those parts.
Centrifugal impact rock crushers generally comprise a horizontal impeller table which rotates about a vertical axis, at a speed which is typically about 1400 RPM, while material to be crushed is fed downwardly onto the center of the impeller table. Impellers mounted on table direct the material radially outward as the centrifugal force created by the rotating table throws the material off of the impellers and against the faces of stationery anvils surrounding the table, where the impact shatters the material into smaller pieces. Since the dust and crushed rock created by the crushing operation is extremely abrasive, the impellers are equipped with replaceable elements called shoes, and the anvils and other portions of the rock crusher exposed to contact with the material being crushed are similarly equipped with replaceable faces or liners.
The impeller table typically includes a central feed cone which rotates with the table to distribute the material among the several impellers to evenly distribute wear of the impeller shoes and loading of the bearings which support the impeller table. When crushing pieces of rock of mixed sizes, the different sized pieces of material generally are thrown radially outward from the cone at different heights corresponding somewhat to the weight of each piece. That is, smaller pieces leave the cone at a higher location than do heavy pieces of rock. As a result, abrasive wear is fairly evenly distributed over the entire wearing surfaces of the impeller shoes, anvils, and other replaceable parts.
A serious problem, however, is presented when a centrifugal rock crusher of this type is used to crush gravel of a fairly uniform size into sand. Gravel or crushed stone which has been graded to contain only pieces of a fairly small variation of size, such as in the size range of 3/8-1/2 inch maximum dimension of each piece, is suitable to be crushed into sand in this type of rock crusher. Crushing material of such a uniform size, however, results in concentrated wear of impeller shoes and anvil face surfaces, since the gravel is consistently being thrown outwardly from the feed cone at about the same height. With a large proportion of the material concentrated near one height relative to the impeller, wear is also concentrated on the surfaces of the impeller shoes and the adjacent anvils at that same height, causing development of a groove along the faces of the impeller shoes and anvils. Such grooves, once started, are self-generating, and eventually require early replacement of impeller shoes and anvil faces, while much of their surfaces are free of appreciable wear.
What is needed therefore is a centrifugal impact rock crusher in which the flow of material to be crushed is distributed over the entire surface of each impeller shoe and anvil face to evenly spread abrasive erosion of internal parts of the rock crusher while crushing material consisting largely of pieces of uniform size.